Relative humidity various

Process Requirements. Typical inside dry-bulb temperatures and relative humidities used for preparing, processing, and manufacturing various products, and for storing both raw and finished goods, are Hsted in Table 1. In some instances, the conditions have been compromised for the sake of worker comfort and do not represent the optimum for the product. In others, the conditions Hsted have no effect on the product or process other than to increase worker efficiency. 

Effective antistatic agents must act at a relative humidity below 40%, preferably below 15%. The agent must form a film on various surfaces and be apphed from a solution or dispersion in water or other inexpensive solvents. The antistatic agent must not interfere with subsequent processing of the product, impair the hand, or affect color, odor, appearance, and performance properties of the substrate. It should be nontoxic and nonflammable. 

Figure 28 shows the key features of the humidity chart. The chart consists of the following four parameters plotted as ordinates against temperature on the abscissas (1) Humidity H, as pounds of water per pound of dry air, for air of various relative humidities (2) Specific volume, as cubic feet of dry air per pound of dry air (3) Saturated volume in units of cubic feet of saturated mixture per pound of dry air and (4) latent heat of vaporization (r) in units of Btu per pound of water vaporized. The chart also shows plotted hiunid heat (s) as abscissa versus the humidity (H) as ordinates, and adiabatic humidification curves (i.e., humidity versus temperature). Figure 28 represents mixtures of dry air and water vapor, whereby the total pressure of the mixture is taken as normal barometric. Defining the actual pressure of the water vapor in the mixture as p (in units of mm of mercury), the pressure of the dry air is simply 760 - p. The molal ratio of water vapor to air is p/(760-p), and hence the mass ratio is ... 

TABLE 12.5 Relative Humidity of Air over Various Saturated Solutions of Salts ... 

Table 26 Relative humidities over various concentrations of sulfuric acid at 20°C.

Conditioning procedures of test specimens and products are important in order to obtain reliable, comparable, and repeatable data within the same or different testing laboratories. Procedures are described in various specifications or standards such as having a standard laboratory atmosphere [50 2% relative humidity, 73.4 1.8°F (23 1°C)] with adequate air circulation around all specimens. The reason for this type or other conditioning is due to the fact the temperature and moisture content of plastics can affect different properties. 

The vapor pressure of water at various temperatures is given in Table 8.3. (a) What is the relative humidity at 30.°C when the partial pressure of water is 25.0 Torr (b) Explain what would be observed if the temperature of the air were to fall to 25°C. 

When pure P-endosulfan was allowed to equilibrate in the apparatus, the ratio of the P-isomer to the a-isomer in the gas phase became 8 92 at 20 , suggesting that the P-isomer converts to the a-isomer (Rice et al. 1997). Several investigators have reported rapid initial losses of endosulfan residues from treated plant surfaces due to volatilization (Archer 1973 Terranova and Ware 1963 Ware 1967). One research group (Willis et al. 1987) attributed the limited runoff losses found in soybean fields treated with endosulfan to early losses of the compound during application and to volatilization/degradation of the compound from plant surfaces. Air sampling performed in a wind tunnel under defined conditions (20 air velocity 1 m/sec relative humidity 40-60%) showed that 60% of the initial dose of endosulfan is volatilized from Trench bean surfaces after 24 hours (Rudel 1997). Influences of various pesticide application formulations were not tested. 

X-ray analysis of the various samples that were produced indicated that the system ZnO-ZnClj-HjO includes four crystalline phases, two of which, ZnO and ZnClj. l HjO, are essentially the starting materials. Sorrell also found the 4 1 5 phase, reported by Droit, with an identical X-ray powder diffraction pattern to that reported by Nowacki Silverman (1961, 1962), and a 1 1 2 phase. Since neither the 1 1 2 nor the 4 1 5 phase lost or gained weight on exposure to air at about 50% relative humidity and 22 °C and no changes developed in the X-ray diffraction pattern following this exposure, he concluded that the previously reported 1 1 1 phase cannot be formulated from mixtures of ZnO and aqueous ZnCl,. 

Cano Barrita [27] cast concrete specimens with w/c of 0.6, dried the specimens at 38 °C and 20% relative humidity, then measured the penetration of water in a capillary uptake type of experiment. A 3D centric scan SPRITE measurement was selected, as an image could be acquired in 150 s and the image would therefore be weighted only by the T2 decay. 3D images were acquired at various exposure times and the central 2D image slice was extracted from the data to measure the penetration depth with time. 

A rational development of models for moisture uptake begins with a description of the experimental procedure used to determine moisture uptake as a function of time. The first step in the experiment is to control the relative humidity to which a sample will be exposed. One technique to control humidity is to use saturated salt solutions. When placed in a closed system and held at a constant temperature, a saturated aqueous salt solution will provide a constant humidity (RH0) within that system. Table 1 lists relative humidities that will be maintained over various saturated salt solutions [14],... 

Humidity is a general term used to refer to water vapor in the air. The actual amount of water vapor that the air can hold increases with the temperature the higher the temperature, the greater the amount of water vapor that the air can hold. Various measures are used to express humidity absolute humidity and relative humidity are the two most widely used. Absolute humidity is the amount (by weight) of water vapor in the air at a particular temperature and pressure and it is usually measured in grams per cubic meter. 

Table 11.2 Water partial pressure and relative humidity under various conditions... 

In order to examine the process of ultrafine particle formation, a joint series of experiments were conducted at the Denver Research Center of the U.S. Bureau of Mines. In the Denver radon chamber, the activity size distribution of the ultrafine mode was measured using the mobility analyzer designed by Chu and Hopke (1985), the separate single screen method (Holub and Knutson, 1987), and the stacked single screen method (Holub and Knutson, 1987) for various relative humidities and for various concentrations of SO. The results... 

Figure 3. Mobility spectra of Po-218 ions at various relative humidities and SO concentrations.

Brittle fracture indices were obtained for a series of compacted direct compression excipients that had been exposed to various degrees of ambient relative humidity [67], As illustrated in Fig. 9, compacts of the essentially... 

Conductive sample coatings are not needed because the gas molecules in the chamber replenish electrons on the sample surface to prevent charging. Direct observation of either wet or dry specimens is possible based on the continuously variable specimen environment. The instrument accommodates a micromanipulator, heatable stage, and gaseous environment. Energy dispersive x-ray (EDX) units can also be added to the sample chamber for elemental analysis. Samples can be analyzed in their natural state, at elevated relative humidities, elevated temperatures, and in various gas environments (including 100% relative humidity). 

It is the objective of this chapter to discuss the various mechanisms whereby water can interact with solid substances, present methodologies that can be used to obtain the necessary data, and then discuss moisture uptake for nonhydrating and hydrating crystalline solids below and above their critical relative humidities, for amorphous solids and for pharmaceutically processed substances. Finally, transfer of moisture from one substance to another will be discussed. 

Earthworm, Aporrectodea caiignosa cocoons exposed to aqueous solutions of copper chloride at 0-20 mg Cu/L for 14 days at 20°C and 100% relative humidity, and then to either desiccation or frost for 14 days No adverse effects at 6 and 12 mg Cu/L. At 20 mg Cu/L, none survived at -3°C and 95% survived at 0°C embryos contained up to 200 mg Cu/kg DW — comparable to concentrations found in various earthworm tissues from copper-contaminated soils 18... 

Because of the long duration and expense of carcinogenicity studies, the care of animals used in these studies is of paramount importance. Various physical and biological factors can affect the outcome of these studies. Some important physical factors include light, temperature, relative humidity, ventilation, atmospheric conditions, noise, diet, housing, and bedding (Rao and Huff, 1990). Biological factors include bacteria and viruses that may cause infections and diseases. 

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